Researchers assemble an all-nanocrystal transistor

Using standard techniques of the trade, chemists can readily synthesize nanometer-sized crystals with tailored semiconducting bandgap, charge mobility, and other electronic properties. Made into inks, the nanocrystals can be deposited on plastic or other flexible substrates at room temperature without the high vacuum required in conventional semiconductor device fabrication. Nanocrystals should thus be ideal building blocks for flexible electronic devices. However, integrating different nanocrystals into a single device—say a field-effect transistor (FET) which is built from conducting, semiconducting, and insulating parts—has been elusive. Researchers can use nanocrystals for one component of a device but resort to conventional vacuum-based deposition to lay down the rest. Now a University of Pennsylvania group led by Cherie Kagan and Christopher Murray has developed a recipe to fabricate FETs entirely from nanocrystals. The researchers sequentially deposited each component: silver nanocrystals for the gate electrode, aluminum oxide for the gate insulator, cadmium selenide for the active semiconductor channel, and a mixture of silver and indium for the source and drain electrodes. The photograph shows, from above, an array of the FETs on a flexible plastic substrate. The inset shows the details of one FET: The Ag/In gate and drain electrodes are separated by 30 μm and the Ag gate electrode is visible below the thin CdSe and Al₂O₃ layers. A set of chemical treatments along the way ensured that the layers don’t delaminate and boosted material properties such as the conductivity of the electrodes and the charge mobility of the semiconductor. Having demonstrated a working all-nanocrystal FET, Kagan and her collaborators are looking to develop printing or some other high-throughput manufacturing process to make the device fabrication practical. (J.-H. Choi et al., Science 352, 205, 2016 .)